In a carding machine, the flat area together with the drum forms the main carding zone and has as its function the breaking down of tufts to form single fibers, the separation of dirt and dust, the elimination of very short fibers, the breaking down of neps, and the parallelization of the fibers. Because of their function, the flats become blocked with dirt and fibers and it is therefore necessary to clean them. For this reason, the revolving flat was developed, wherein the flats are held together by means of a chain or belt and combined to form an endless, rotating strip. During a rotation of the flats, also referred to as the flat passage, part of the flat is always in direct use opposite the drum fittings. The remaining part of the flat is transported back face upwards over deflector rollers and can be cleaned and, if necessary, ground during this phase.
A narrow gap, known as the carding gap, is formed between the fittings of the flat and the fittings of the drum. This is produced in that the revolving flats, guided by means of curved strips, so-called flexible arcs, are guided along in the circumferential direction of the drum at a distance from one another determined by these flexible arcs. In a revolving flat carding machine, the size of the carding gap lies between 0.10 to 0.30 mm for cotton or up to 0.40 mm for chemical fibers. Precise guiding of the revolving flats by the flexible arcs is therefore of central importance. The carding gap must also be of uniform size over the whole working width of a carding machine in order to achieve good carding performance. This places high demands on the linearity and the dimensional stability of the revolving flats.
The head end pieces of the revolving flats rest on the flexible arc on both sides of the carding machine. To enable these head end pieces to be accurately guided on the surface of the flexible arcs, the running surface of the head end pieces which faces the flexible arc is adjusted in shape to match the radius of the guide surface of the flexible arcs. The running surfaces of the head end pieces are subject to wear over an extended operating period. This is rectified by periodically re-machining the running surfaces. Revolving flats which have head end pieces with replaceable slide elements, so-called sliding shoes, are known from the prior art. However, when these slide elements are changed, it is also necessary to match the shape of their running surfaces to the flexible arc.
It is known from the prior art to machine the running surfaces of the head end pieces with a cylindrical milling cutter which is moved at right angles to the longitudinal axis of the revolving flat. DE 634 651 shows a device for grinding the contact surfaces at the ends of head end pieces with a grinding disc. With both methods, machining the running surfaces of the head end pieces leads to a flat shape of the running surfaces. At the same time, the flat running surface created by machining is parallel to the plane of the contact surface of the fittings. The disadvantage is that, in operation, the revolving flat with a flat running surface has to be guided over a flexible arc which has a radius. This results in a linear contact of the revolving flat on the flexible arc, which leads to inaccurate guiding of the revolving flat and increased wear of the running surfaces of the revolving flat.
DE 42 43 807 discloses a device for checking the flatness of a revolving flat. For this purpose, the flat bar with the running surfaces is placed on bearing blocks and measured at a plurality of measuring points over its length. The measurements are evaluated by a computer and the flatness of the revolving flat determined therefrom. A decision can be made relating to the further use of the revolving flat based on the evaluation.